1. Field of the Invention
The present invention relates to a method of avoiding an error of a pointer process in an SDH (synchronous digital hierarchy) transfer system and to a SDH radio communication device.
In recent years, a number of SDH networks have been implemented based on optical fibers, and, also, use of SDH systems has been on increase in digital multiplex radio systems. Against this background, it is vital to provide for SDH radio devices in implementing an SDH network where these SDH radio devices are equipped with stable high-quality data-transfer functions complying with the SDH interface. Also, a configuration that insures no malfunction is expected.
2. Description of the Related Art
FIG. 1 is an illustrative drawing showing a configuration of radio devices complying with the SDH interface. The configuration includes a carrier device 16-1 of an SDH transfer system, radio devices 16-2 and 16-3 complying with the SDH interface, and a carrier device 16-4 of another SDH transfer system.
The carrier devices 16-1 and 16-4 are connected to the radio devices 16-2 and 16-3, respectively, via optical cables conveying optical signals or coaxial cables or the like for conveying electrical signals. The radio devices 16-2 and 16-3 are connected to each other by means of a radio communication line. In this radio communication line, a radio frame complementary overhead (RFCOH) is attached when transfer is engaged.
FIG. 2 is an illustrative drawing for explaining a main portion of the radio device complying with the SDH interface. FIG. 2 is used for explaining a main portion of the radio device 16-2 or 16-3.
The radio device in FIG. 2 includes a carrier-side SDH-physical-interface (SPI) unit 17-1, a carrier-side regenerator-section-overhead (RSOH) processing unit 17-2, a carrier-side multiplex-section-overhead (MSOH) processing unit 17-3, a carrier-side administrative-unit-pointer (AU pointer) processing unit 17-4, a radio-side administrative-unit-pointer (AU pointer) processing unit 17-5, a radio-side multiplex-section-overhead (MSOH) processing unit 17-6, a radio-side regenerator-section-overhead (RSOH) processing unit 17-7, a modem 17-8, and a radio-transmission/reception unit (TX/RX) 17-9. A carrier-side processing unit is designated as 17-10, and a radio-side processing unit is denoted as 17-11. Here, an antenna for radio transmission/reception is not shown-in the figure.
The carrier-side SDH-physical-interface unit 17-1 is an interface for exchanging optical/electrical signals with the carrier device 16-1 or 16-4. The carrier-side regenerator-section-overhead processing unit 17-2, the carrier-side multiplex-section-overhead processing unit 17-3, and the carrier-side administrative-unit-pointer processing unit 17-4 are used for exchanging data with the carrier device of the SDH transfer system by using a STM-1 frame format, for example.
The SDH transfer system transfers digital signals by use of a standard STM (synchronous transfer mode) frame format. In this case, the STM-1 frame format (155 Mbps), for example, includes a section overhead (SOH) having 9 rows each comprised of 9 bites and a payload having 9 rows each comprised of 261 bytes.
FIG. 3 is an illustrative drawing showing a STM-1 frame format. A section overhead (SOH) 18-1 includes frame-synchronization bytes A1 and A2, an STM-frame-identification byte J0, error monitoring bytes B1 and B2, maintenance-personnel-voice-talk bytes E1 and E2, a user-channel byte F1, data-communication-channel bytes D1 through D12, pointer bytes H1 and H2, stuff-operation bytes H3, a switch-control byte K1, a section-warning-display byte K2, a synchronization-clock-quality byte S1, and a error-notification byte M1. A regenerator-section overhead is denoted as RSOH, and a multiplex-section overhead is denoted as MSOH. Further, a portion which stores bytes H1, H2, and H3 is referred to as an AU-pointer portion.
FIGS. 4A and 4B are illustrative drawings for explaining the pointer bytes H1 and H2, respectively. The pointer bytes H1 and H2 include 4 bits of new-data flags (NDF) N, SS bits, and a 10-bit pointer comprised of bits I and D.
The 4-bit new-data flags N are used for transferring an NDFEN signal (e.g., 1001) indicative of a change in a pointer value or an NORNDF signal (e.g., 0110) indicative of no change in the pointer value.
The 2-bit SS bits are used for detecting an invalid pointer. In detail, a set value or a fixed value is sent from a transmitter side, and a receiver side compares received SS bits with the set value or the fixed value in order to detect an invalid pointer.
The 10-bit pointer containing a pointer value is comprised of 5 bits of bit I and 5 bits of bit D arranged in turn at every other position, and is used for indicating a start position of multiplexed data in the payload as well as for controlling stuff operations.
The payload 18-2 comprised of 9 rows of 261 bytes stores data starting from a selected one of positions provided at 3-byte intervals. A position of the first data (J1 bytes) in the payload is represented by the 10-bit pointer indicative of one of 0 through 782.
The 10-bit pointer included in the pointer bytes H1 and H2 indicates the position of the first data in the payload, and, also, is used for controlling stuff operations. The stuff operations include a positive stuff operation inserting 3-byte stuff bytes into the payload and a negative stuff operation relocating 3-byte data from the payload to the stuff-operation bytes H3#1 through H3#3 in the AU-pointer portion.
The 5 bits I in the 10-bit pointer are used when the positive stuff operation is performed. In the case of the positive stuff operation, the transmitter side obtains an inverse of each of 5 bits I of a preceding frame, and sends each of the obtained inverses as a bit I. By doing so, the transmitter side indicates an increment by 3 bytes of the position of the first data in the payload, and inserts 3 stuff bytes into the payload before transmitting an STM-1 frame signal.
The 5 bits D in the 10-bit pointer are used when the negative stuff operation is performed. In the case of the negative stuff operation, the transmitter side obtains an inverse of each of 5 bits D of a preceding frame, and sends each of the obtained inverses as a bit D. By doing so, the transmitter side indicates a decrement by 3 bytes of the position of the first data in the payload, and relocates 3-byte data from the payload to the stuff-operation bytes H3#1 through H3#3 in the AU-pointer unit before transmitting an STM-1 frame signal.
The receiver side checks the pointer bytes H1 and H2, and accept them as a correct pointer indicative of the position of the first data in the payload if the pointer value represented by the 10 bits is identical in more than two consecutive frames. Because of this, even when bits I and bits D of the 10-bit pointer are used for the stuff operations, the pointer value can never be misidentified as indicating a wrong position of the first data in the payload.
Further, if no less than 3 bits I out of the total of 5 bits I are an inverse of respective bits I of the preceding frame and if no more than 2 bits D out of the total of 5 bits D are an inverse of respective bits D of the preceding frame, a determination is made that a positive stuff operation has been conducted. In this case, processing of the received payload data is carried out such that the stuff bytes inserted on the transmitter side are not read on the receiver side.
Further, if no less than 3 bits D out of the total of 5 bits D are an inverse of respective bits D of the preceding frame and if no more than 2 bits I out of the total of 5 bits I are an inverse of respective bits I of the preceding frame, a determination is made that a negative stuff operation has been conducted. In this case, the receiver side reads data from the stuff-operation bytes H3#1 through H3#3 in the AU-pointer portion as well as the payload data, and processes the data.
As described above, the pointer bytes H1 and H2 indicate a start position of the multiplex data in the payload, and, also, indicates presence/absence of a stuff operation through inverting of bits in the pointer. As shown in the STM-1 frame format of FIG. 3, the pointer bytes H1 and H2 are arranged next to each other in a concentrated manner in the section overhead (SOH) 18-1. Because of this arrangement, when a transfer error of a burst type is generated with respect to the pointer bytes H1 and H2, the pointer value will be misidentified, and the start position of the multiplex data in the payload cannot be correctly identified. Namely, an erroneous pointer process may be performed.
FIGS. 5A and 5B are illustrative drawings for explaining a burst error which will affects a pointer process. FIG. 5A shows a case in which a burst error occurs in the payload and the pointer byte H1#1. FIG. 5B shows a case in which a burst error is generated in the section overhead SOH including the pointer bytes H1#1.
As shown in FIGS. 5A and 5B, if a burst error hits the new-data flags N and the bits I and D constituting a 10-bit pointer, the receiver side may receive the NDFEN (NDF enable) signal (e.g., 1001) indicative of a change in the pointer value, and may mistakenly update the pointer value based on the false 4 indication of the change.
FIGS. 6A and 6B are illustrative drawings for explaining a burst error which will affect a stuff operation. FIG. 6A shows a case in which a burst error hits among other portions a portion including at least three bits I of the bits I and D of the 10-bit pointer. FIG. 6B demonstrates a case in which a burst error is generated with respect to a portion including at least three bits D in addition to other portions.
If a burst error damages at least 3 bits I or at least 3 bits D, the receiver side ascertains that conditions indicating a proper stuff operation are satisfied, and mistakenly attends to a stuff operation.
A transfer error of a burst type is likely to occur in radio communication lines where so-called phasing or the like is brought about as a irregular communication fault when radio waves interfere with each other because of reflections and diffractions and suffer a severe attenuation in magnitude. Once such a transfer error of a burst type develops, dozens of consecutive bits are damaged by the error. If the transfer error of a burst type develops in the pointer bytes H1 and H2 which are closely arranged, the pointer value may be misidentified, and the pointer process and the stuff operation on the receiver side may not be properly conducted.
The STM-1 frame format is defined by ITU-T (international telecommunication union telecommunication standardization sector), so that no arbitrary change can be made thereto. Further, there is no guarantee that the carrier device 16-1 and the radio device 16-2 used for implementing the network are manufactured as one set of devices. Because of this, an arrangement of the AU-pointer portion attended to by the carrier-side administrative-unit-pointer processing unit 17-4 (FIG. 2) needs to be in compliance with the standard format as stipulated in ITU-T.
A format used in the radio section between the radio devices 16-2 and 16-3 may be in accordance with the SDH format. In this case, as noted previously, the radio-frame-complementary overhead RFCOH may be attached. Fortunately, the SDH format contains unused bytes.
Accordingly, there is a need for a scheme which can reduce a likelihood of an erroneous pointer process caused by a transfer error of a burst type by use of unused or undefined bytes of the section overhead SOH in the radio-frame-complementary overhead or the SDH format.
Accordingly, it is a general object of the present invention to provide a device and a method which can satisfy the need described above.
It is another and more specific object of the present invention to provide a device and a method which can reduce a likelihood of an erroneous pointer process caused by a transfer error of a burst type by use of unused or undefined bytes of the section overhead SOH in the radio-frame-complementary overhead or the SDH format.
In order to achieve the above objects according to the present invention, a method of preventing an error of a pointer process in an SDH radio device which receives an STM frame having a section overhead and a payload therein includes the steps of distributing a pointer to unused bytes or undefined bytes in the section overhead of the STM frame, the pointer indicating a start position of multiplex data in the payload of the STM frame, and transmitting the STM frame to the SDH radio device.
In the method described above, a pointer as originally included in the STM frame can be reconstructed on the receiver side by extracting the distributed pointer from the STM frame. Because of the distributed arrangement of the pointer, a likelihood of an error of a pointer process can be reduced when a burst error is generated.
According to another aspect of the present invention, a method of preventing an error of a pointer process in an SDH radio device which receives an STM frame having a section overhead and a payload therein along with radio-frame-complementary overheads attached to the STM frame includes the steps of distributing a pointer in the radio-frame-complementary overheads attached to the STM frame, the pointer indicating a start position of multiplex data in the payload of the STM frame, and transmitting the STM frame to the SDH radio device.
In the method described above, the pointer is distributed in the radio-frame-complementary overheads, which are used only for a radio-communication section. Because of the distributed arrangement of the pointer, the pointer can be reconstructed even when a burst error occurs, thereby reducing a likelihood of an error of a pointer process.
According to another aspect of the present invention, a method of preventing an error of a pointer process in an SDH radio device which receives an STM frame having a section overhead and a payload therein includes the steps of generating stuff-check bits indicative of a type of a stuff operation based on a pointer indicating a start position of multiplex data in the payload of the STM frame, distributing the stuff-check bits to unused bytes or undefined bytes in the section overhead of the STM frame in addition to allocating the pointer to a standard position thereof in the section overhead of the STM frame, and transmitting the STM frame to the SDH radio device.
In the method described above, the stuff-check bits-can be reconstructed even when a burst error occurs, thereby reducing a likelihood of an error of a pointer process including a stuff process.
According to another aspect of the present invention, a method of preventing an error of a pointer process in an SDH radio device which receives an STM frame having a section overhead and a payload therein along with radio-frame-complementary overheads attached to the STM frame includes the steps of generating stuff-check bits indicative of a type of a stuff operation based on a pointer indicating a start position of multiplex data in the payload of the STM frame, distributing the stuff-check bits to the radio-frame-complementary overheads attached to the STM frame in addition to allocating the pointer to a standard position thereof in the section overhead of the STM frame, and transmitting the STM frame to the SDH radio device.
In the method described above, the stuff-check bits can be reconstructed even when a burst error occurs, thereby reducing a likelihood of an error of a pointer process including a stuff process.
According to another aspect of the present invention, a method of preventing an error of a pointer process in an SDH radio device which receives an STM frame having a section overhead and a payload therein along with radio-frame-complementary overheads attached to the STM frame includes the steps of distributing a plurality of pointers in the radio-frame-complementary overheads attached to the STM frame in addition to allocating a pointer in the section overhead of the STM frame, the pointers being identical to the pointer which indicates a start position of multiplex data in the payload of the STM frame, transmitting the STM frame to the SDH radio device, and taking a majority vote among the plurality of pointers and the pointer on a side of the SDH radio device.
In the method described above, a correct pointer can be identified by the majority vote even when a burst error occurs, thereby reducing a likelihood of an error of a pointer process.
According to another aspect of the present invention, a method of preventing an error of a pointer process in an SDH radio device which receives an STM frame having a section overhead and a payload therein includes the steps of receiving a pointer indicative of a start position of multiplex data in the payload of the STM frame and indicative of a type of a stuff operation, the start position depending on the type of a stuff operation, making a first check regarding the type of a stuff operation based on the pointer, making a comparison of a set of data extracted from the payload at the start position of multiplex data over a predetermined number of STM frames with a predetermined set of expected data, the comparison being made with respect to each of different start positions corresponding to different types of stuff operations, and making a second check to identify the type of the stuff operation based on the first check and the comparison.
In the method described above, protection against an error in a stuff check can be provided, thereby reducing a likelihood of an error of a pointer process including a stuff process when a burst error is generated.
Each of the methods described above can be implemented by a respective device as shown in the following.
According to one aspect of the present invention, a device for conducting radio communication based on an SDH system by exchanging an STM frame having a section overhead and a payload therein includes a pointer-arrangement-conversion unit which arranges each bit of a pointer in such an arrangement as to correspond to unused bytes or undefined bytes in the section overhead of the STM frame, the pointer indicating a start position of multiplex data in the payload of the STM frame, a frame-memory unit which accumulates at least one STM frame""s worth of data, and a pointer-multiplex unit which multiplexes the pointer to the STM frame supplied from the frame-memory unit so as to distribute the pointer to the unused bytes or undefined bytes in the section overhead of the STM frame.
According to another aspect of the present invention, a device for conducting radio communication based on an SDH system by exchanging an STM frame having a section overhead and a payload therein includes a radio-frame-complementary-overhead-multiplex unit which attaches radio-frame-complementary overheads to the STM frame, a pointer-demultiplex unit which extracts from the STM frame a pointer indicative of a start position of multiplex data in the payload of the STM frame, and a pointer-multiplex unit which distributes the pointer extracted by the pointer-demultiplex unit to the radio-frame-complementary overheads attached to the STM frame by the radio-frame-complementary-overhead-multiplex unit.
According to another aspect of the present invention, a device for conducting radio communication based on an SDH system by exchanging an STM frame having a section overhead and a payload therein includes a stuff processing unit which performs a stuff operation, and generates stuff-check bits corresponding to the stuff operation based on a pointer indicative of a start position of multiplex data in the payload of the STM frame, and a stuff-check-bit-multiplex unit which distributes the stuff-check bits to unused bytes or undefined bytes in the section overhead of the STM frame, wherein the pointer is allocated to a standard position thereof in the section overhead of the STM frame.
According to another aspect of the present invention, a device for conducting radio communication based on an SDH system by exchanging an STM frame include a stuff-information-extraction unit which extracts stuff-check bits corresponding to a stuff operation from the STM frame, a radio-frame-complementary-overhead-multiplex unit which attaches radio-frame-complementary overheads to the STM frame, and a stuff-check-bit-multiplex unit which distributes the stuff-check bits extracted by the stuff-information-extraction unit to the radio-frame-complementary overheads attached to the STM frame by the radio-frame-complementary-overhead-multiplex unit.
According to another aspect of the present invention, a device for conducting radio communication based on an SDH system by exchanging an STM frame having a section overhead and a payload therein includes a pointer-demultiplex unit which extracts from the STM frame a pointer indicative of a start position of multiplex data in the payload of the STM frame, a radio-frame-complementary-overhead-multiplex unit which attaches radio-frame-complementary overheads to the STM frame, a pointer-multiplex unit which allocates a plurality of pointers to the radio-frame-complementary overheads attached to the STM frame by the radio-frame-complementary-overhead-multiplex unit, the plurality of pointers identical to the pointer, a receiver-side pointer-demultiplex unit which extracts the plurality of pointers from received radio-frame-complementary overheads sent from another device for conducting radio communication, a pointer-byte-demultiplex unit which extracts the pointer from a received STM frame sent from the another device, and a pointer-byte-majority-vote unit which takes a majority vote among the plurality of pointers extracted from the received radio-frame-complementary overheads and the pointer extracted form the received STM frame.
According to another aspect of the present invention, a device for conducting radio communication based on an SDH system by exchanging an STM frame having a section overhead and a payload therein includes a pointer-demultiplex unit which extracts a pointer indicative of a start position of multiplex data in the payload of the STM frame and indicative of a type of a stuff operation, the start position depending on the type of a stuff operation, a first stuff-check unit which makes a first check regarding the type of a stuff operation based on the pointer, a comparison unit which makes a comparison of a set of data extracted from the payload at the start position of multiplex data over a predetermined number of STM frames with a predetermined set of expected data, the comparison being made with respect to each of different start positions corresponding to different types of stuff operations, and a second-check unit which makes a second check to identify the type of the stuff operation based on the first check and the comparison.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.